Abstract: Abstract: To explore the effect of polyaluminum chloride (PAC) of different concentrations in coal flotation, flotation rate experiments were conducted with the mixture of coal (250-125 μm) and kaolinite(- 100 μm). Water recovery, gangue recovery, entrainment index, Efficiency Index (EI), Separation Efficiency Rate (SER), and Se-lectivity Index (SI) were used to evaluate flotation performance. The experimental results show that the addition of PAC can reduce water recovery, gangue recovery and entrainment index. The three flotation evaluation indexes (EI, SER, and SI) showed that the optimum flotation efficiency was obtained when the PAC concentration was 20mg/L. PAC of different concentrations was used to agglomerate kaolinite, and the unweighted chord length distribution of kaolinite suspensions was measured by the Focused Beam Reflectance Measurement (FBRM). FBRM measurements showed that with the increase of PAC concentration, the chord length distributions of kaolinite increased first reaching the peak at 20 mg/L and then decreased. Bubble-particle attachment probability measurements were car-ried out with the coal which was interacted with PAC of different concentrations. The bubble-particle attachment probability measurements showed that PAC reduced the hydrophobicity of coal particles, which matched well with the reduction of flotation rate.